The present invention relates to a transmission line at least a part of which is composed of a dielectric material such as a dielectric line, surface wave line (including image line, insular line), a metallic wave guide tube lined with a dielectric material, and combinations thereof.
Waves in the frequency regions of millimeter waves, sub-millimeter waves and light waves are transmitted in one of the dielectric internal modes, either surface wave mode, wave guide tube mode or suitable combinations thereof. A transmision line making use of a dielectric material has high flexibility so that it can suitably be used in the flexed part of a metallic wave guide tube or in the connection between a metallic wave guide tube and associated equipment. A transmission line employing a dielectric material is attracting attention even in the form of a single line because it can be laid with a large degree of freedom at small radius of curvatures. In a transmission line having dielectric body, a problem is encountered because the direction of the electric field (or direction of the magnetic field) can be rotated undesirably. Namely, when a connection between transmission lines or between transmission line and equipment is made using this type of transmission line, even if the lines are independently adjusted to provide a connection to attain maximum output energy level for a given input level, the level of output is inevitably changed as the lines are moved or as time lapses.
Used those circumstances, the present invention provides a transmission line in which at least a portion thereof is composed of a dielectric body which overcomes the above-described problem of prior art transmission lines.